U-type two-cycle engine



Oct. 18, 1938. G. E. A. HALLETT U-TYPE TWO-CYCLE ENGINE Filed Oct. 30. 1936 Patented Oct. 18, 1938 PATENT OFFICE U-TYPE TWO- CYCLE ENGINE George E. A. Hallett, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application October 30, 1936, Serial No. 108,343

4 Claims.

This invention relates to so called U type two cycle engines in which a pair of parallel cylinders have a common combustion chamber, one of the cylinders being provided with inlet ports and the other with exhaust ports opened and closed by the pistons, towards the end of their power stroke and the beginning of their compression stroke. The inlet and exhaust pistons move together in the same direction, but it is usual for the exhaust piston to. have a slight lead on the inlet piston.

In such an engine, any residual exhaust gases which remain in the exhaust cylinder after the exhaust port has been closed on the compression stroke are carried upwards into the combustion chamber and are to some extent pumped into the combustible charge in the combustion chamber. The actual quantity so pumped and its influence will depend on the amount of charge admitted through the engine inlet ports, particularly when scavenging is effected solely by the incoming combustible charge.

At low load, or when idling, when only a small quantity of charge is admitted, the larger pro- 5 portion of burnt gases remaining in the engine, dilutes the combustible gases to the point where it is difiicult to fire the charge.

It is especially difficult to secure proper idling with a small economical charge in an engine 30 having an ideal combustion chamber in other respects, with a quench area over the exhaust piston, due to the fact that burnt gases are squirted from such a quench area into the idling charge by the exhaust piston when the exhaust piston has a lead on the inlet piston and reaches top dead center before the inlet piston.

The object of the present invention is a means of providing for the segregation of a small idling charge of fresh mixture away from the contami- 0 nating influence of the burnt charge, and at a point where it can be effectively fired by the igniting means, thus to maintain the engine in operation without stopping, on smaller charges than has heretofore been possible for the reasons aforegiven.

The above and other objects of the invention will be apparent as the description proceeds.

According to the invention a step is provided, forming a pocket in the head of the inlet piston, on that side thereof farthest away from the exhaust piston.

The inlet ports in the cylinder wall are stepped in conformity with the step in the inlet piston so that all the ports in the inlet cylinder wall will be closed and opened at the same time by the piston in its stroke movement.

Directly over the pocket the cylinder head is stepped slightly so as to efl'ect almost complete closure and segregation of the pocket from the 5 combustion chamber proper, when the exhaust and inlet pistons are towards the end of their compression stroke.

A spark plug is provided in the cylinder head to fire the idling charge in the pocket, and a second spark plug may be placed in the most advantageous position to fire the main part of the charge in the combustion chamber, at greater loads and speeds other than idling.

The drawing shows the application of the invention to a U type 2-cycle engine.

In the drawing, Figure l is a part sectional elevation of the pistons, cylinders, and combustion chamber. Figure 2 is a diagrammatic end view showing the pistons and their connecting rods to the crank shaft. Figure 3 is a view on line 3--3 of'Figure l to a reduced scale.

In the drawing, the cylinder block I is provided with a cylinder 2, having inlet ports 3 and a cylinder 4, having exhaust ports 5, these ports being controlled respectively by pistons 6 and 1.

A pocket 8 is formed by a stepped down portion in the head of the inlet piston 6.

The cylinder head 9 has a combustion chamber l0, common to the two cylinders 2 and 4, there being a quench area ll over the exhaust piston 1, and a slightly stepped down portion ll of the cylinder head forming a lip cooperating with the stepped down portion in the inlet piston, to effect segregation of a part of the fresh charge in the pocket 8, more or less separated from the combustion chamber proper, when the exhaust and inlet pistons are at'the end of their compression stroke.

I3 is a spark plug for igniting the charge in the pocket 8, while the spark plug I4 is advantageously placed for igniting the main part of the charge in the combustion chamber at higher loads and speeds.

It will be noted that the inlet ports 3 are stepped to conform with the irregular contour of the head of the inlet piston 6.

The pistons 6 and 1 are shown in a position corresponding to the top dead center position of the piston I, the piston 6 not having yet reached this position. It can clearly be seen that in this condition the exhaust piston will be compressing and squirting some of the contents of cylinder 4 from the quench area H across the combustion chamber. Without the pocket 8, and when, as 55 2 in idling, the contents of cylinder 4 being mainly burnt gases and only a small quantity of fresh charge having been admitted into cylinder 2, these burnt gases would disperse and dilute the fresh charge to an extent making it very difficult if not impossible to ignite. The pocket 8, on the other hand, in conjunction with the lip l2 of the cylinder head, effectively segregates part or the whole of the idling charge from the main portion of the combustion chamber, the lip l2, deflecting away from the pocket 8, the burnt gases squirted across the combustion chamber from the quench area I l by the exhaust piston fl.

I claim:

1. In a U type two cycle engine having a cylinder head with a combustion chamber common to two cylinders respectively provided with inlet and exhaust ports, an inlet piston ,in the inlet cylinder and an exhaust piston in the exhaust cylinder, a pocket formed by a step in the head of the inlet piston, on that side thereof farthest away from the exhaust piston, said pocket cooperating with the inlet ports to carry a small idling charge of fresh mixture towards the combus tion chamber on the compression strokemovemerit of the inlet piston, .a lip on the cylinder head coacting with the pocket as the inlet piston approaches the end of its compression stroke,

to segregate the small idling charge away from the diluting influence of the burnt gases compressed into the combustion chamber by the exhaust piston, and a spark plug in the cylinder head, to enter the pocket as the inlet piston reaches the end of its compression stroke, to fire the idling charge 2. The combination according to claim 1 in which the inlet ports in the cylinder wall are stepped in conformity with the step in the inlet piston, so that all the ports in the inlet cylinder will be closed and open at the same time by the inlet piston in its stroke movement.

3. The combination according to claim 1, in which the combustion chamber has a quench area over ,the exhaust piston, and the lip on the cylinder head serves to deflect away from the pocket, the burnt gases squirted across the combustion chamber from the quench area, by the exhaust piston, as it approaches the end of its compression stroke.

1. ljhe combination according to claim 1 having a secondsparkplu" in th'e combustion chamber, at a point remojed from thelpocket tame the main part of the charge in }the combustion chamber at greater loads and speeds other than in c GEORGE E. A. neLLETT. 

